1. Field of the Invention
This invention relates to a process for treating waste incineration flyash and an apparatus therefor. More particularly, it relates to an apparatus and process for treating waste incineration flyash, for reducing particularly toxic organic chlorine compounds contained in waste incineration flyash (hereinafter referred to as flyash) formed at the time of incinerating municipal, commercial, or industrial waste.
2.Description of the Related Art
It has been known that organic chlorine compounds are harmful to human bodies, particularly aromatic chlorine compounds such as highly poisonous aromatic chlorine compounds e.g. PCDD (polychlorinated dibenzo-p-dioxine), PCDF (polychlorinated dibenzofuran), etc. that are formed as by-products of pesticides or secondary-formed substances of waste incineration and that contaminate the environment (K. Olie et al, Chemosphere, 6, 455 (1977), and T. Wakimoto et al, Environmental Health Perspectives, 59, 159 (1985)).
FIG. 4 shows a flow chart of a conventional and typical waste incineration plant. This plant is composed mainly of an incinerator 31 and a gas cooling tower 32, a precipitator 33 and a chimney 34, successively connected to the incinerator. Wastes are subjected to incineration in the incinerator 31 at about 750.degree. to 900.degree. C., and the resulting exhaust gas is cooled down to about 300.degree. C. at the cooling tower 32, introduced into the precipitator 33, and separated into flyash and gas, the flyash being discharged from a flyash-discharging port 33A and the gas being discharged from the chimney 34 to the outside of the system.
However, the above-mentioned process is directed only to removal of solids (mainly, flyash) in exhaust gas discharged from the incinerator, but the removal of toxic organic chlorine compounds, particularly aromatic chlorine compounds, has not yet been taken into consideration.
The present inventors have proposed various proposals for reducing organic chlorine compounds discharged from waste incineration plants.
Firstly, in the previous patent application (Japanese patent application No. Sho 62-70936), the applicants elucidated a generation process of aromatic chlorine compounds and disclosed a process for preventing the occurrence of the same. This process was sufficiently effective for inhibiting the occurrence of organic chlorine compounds, but the processing of once generated chlorine compounds has still not been taken into consideration.
In Japanese patent application laid-open No. Hei 1-155937, the applicants proposed a process for removing aromatic chlorine compounds contained in exhaust gas generated from waste incinerators. According to this technique, aromatic chlorine compounds contained in exhaust gas are notably reduced, but organic chlorine compounds separated from exhaust gas and contained in flyash have not been removed.
Thus, there is a fear that organic chlorine compounds such as the above PCDD, PCDF, etc. are included in flyash discharged from an electric precipitator (EP) and other dust-removing means equipped in the waste incineration apparatus. Further, when the flyash is dumped in landfills for example, there is a danger that the organic chlorine compounds return via leachate and the like to animals, plants or human bodies to have a bad effect upon them.
Thus, in Japanese patent application No. Sho 63-147193, the applicants proposed a technique of reducing toxic organic chlorine compounds, particularly aromatic chlorine compounds, contained in flyash, but it is still insufficient.